<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <form id="submit">
        <p><input type="text"></p>
        <input type="submit" name="" id="">
    </form>
    <script>
        //当表单的submit按钮被按下时，表单会触发submit事件
        var submit = document.getElementById("submit");
        submit.onsubmit = function(){
            alert(1);
        }
    </script>
</body>
</html>